During a combustion process of an internal combustion engine, gasoline is oxidized and hydrogen (H) and carbon (C) combine with air. Various chemical compounds are formed including carbon dioxide (CO2), water (H2O), carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (HC), sulfur oxides (SOx), and other compounds.
A vehicle exhaust system includes a catalytic converter that reduces CO, HC, and NOx in the exhaust gas. Efficiency of the catalytic converter is periodically monitored to prevent excess CO, HC, and NOx in the exhaust gas. Typically, the catalytic converter is monitored during steady state engine operation. At idle, for example, an engine control module adjusts an air to fuel (A/F) ratio to achieve consistent emissions output.
Traditional monitoring methods force the A/F ratio to one of a lean or rich condition for a predetermined period. The control module switches the A/F ratio back to either a rich or lean condition after expiration of the predetermined period. During the predetermined period, the control module estimates an oxygen storage capacity (OSC) of the catalytic converter based on a lag time between an inlet oxygen sensor and an outlet oxygen sensor detecting the lean/rich condition. The OSC is indicative of the efficiency of the catalytic converter.
Existing catalytic converter monitoring devices and methods are not effective for use with water-cooled exhaust systems, as are typically used in marine vehicles. For example, the outlet oxygen sensor can be rendered inoperable due to a high moisture content found in marine exhaust systems.